1. Field of the Invention
The present invention relates to a printer, and more particularly, to a printer comprising a plurality of electrode arrays for forming an electrostatic image onto an image roller of the color printer, the electrostatic image capable of attracting toner contained in a toner cartridge of the color printer and forming a printed image.
2. Description of the Prior Art
Please refer to FIG. 1, which is a schematic diagram of a laser printer 10 according to the prior art. The laser printer 10 comprises a housing 71 (not shown), an image roller 12 rotatably installed inside the housing 71, a charged roller 14 for disposing positive charges onto the image roller 12, a laser beam unit 16 for emitting laser beams onto the image roller 12, a toner cartridge 18 containing toner, a developer roller 20 installed on a side of the toner cartridge 18 capable of attracting toner contained in the toner cartridge 18, a transfer roller 22 electrically connected to a negative bias voltage (not shown), a fuser 24 for melting plastic components of the toner contained in the toner cartridge 18, and a discharge unit 26 for cleaning charge residues on the image roller 12.
Principles and operations of the laser printer 10 are briefly described as follows: The charged roller 14 disposes positive (or negative) charges onto the image roller 12. The laser beam unit 16 emits laser beams of a variety of levels onto a predetermined region of the image roller 12. Since the image roller 12 is made of photoconductive material, when the predetermined region of the image roller 12 receives the laser beams emitted by the laser beam unit 16, the charges initially disposed on the predetermined region are affected by photons of the laser beams and trigger the photoconductive material to conduct and discharge, forming an electrostatic image of a relative low level on the predetermined region. A voltage at a point of the electrostatic image relates to power of a laser beam received by the point. That is, the higher the power of the laser beam, the larger a voltage difference of the point becomes; on the contrary, the lower the power of the laser beam, the smaller the voltage difference of the point becomes. After a while, when the image roller 12 rotates to a position where the electrostatic image is adjacent to the developer roller 20, since the develop roller 20 has attracted toner contained in the toner cartridge 18, the electrostatic image of an appropriate level is capable of attracting the toner on the developer roller 20. The larger the voltage difference of the electrostatic image is, the more toner the electrostatic image can attract, and vice versa. When the image roller 12 proceeds to rotate to another position where the electrostatic image is adjacent to the transfer roller 22, since the transfer roller 22 is connected with a negative bias voltage, which is lower than voltages at all points of the electrostatic image (the absolute value of the negative bias voltage is higher than the absolute values of voltages at all points of the electrostatic image), the transfer roller 22 is capable of attracting all the toner on the electrostatic image to a printing media 11 disposed between the transfer roller 22 and the image roller 12. The toner is now temporarily disposed on the printing media 11 due to electrostatic force of the toner only, so any impact (external force, etc) to the laser printer 10 can disturb the toner. After the printing media 11 passing through the fuser 24, the heat that the fuser 24 generates melts the plastic material of the toner and adheres the melted toner onto the printing media 11. When the transfer roller 22 has transferred toner on the electrostatic image onto the printing media 11 and the image roller 12 rotates to a position where the electrostatic image is adjacent to the discharging unit 26, the discharging unit 26 discharges charges of the electrostatic image completely such that the image roller 12 can regain charges disposed by the charged roller 14 when rotating to a position adjacent to the charged roller 14.
The laser beam unit 16 of the laser printer 10 comprises a laser unit 17 for emitting laser beams by determining page data, and a movable mirror 19 for reflecting the laser beams emitted by the laser unit 17 onto the predetermined region of the image roller 12. The laser beam unit 16 requires a high-quality laser unit 17 for emitting beams onto the predetermined region precisely.
The laser printer 10 shown in FIG. 1 is a black-and-white laser printer. Please refer to FIG. 2, which is a schematic diagram of a Carousel color laser printer 30 according to the prior art. The color laser printer 30 comprises an image roller 32, a charged roller 34, a laser beam unit 36, a transfer roller 42, a fuser 44, and a discharging unit 46. A printing media is disposed between the image roller 32 and the transfer roller 42. Different from the laser printer 10, the color laser printer 30 comprises four sets of toner cartridges 38Y, 38C, 38M and 38K containing yellow, cyan, magenta and black toner, and four corresponding developer roller 40Y, 40C, 40M and 40K.
The color laser printer 30 has principles and operations similar to those of the black-and-white laser printer 10. The only difference is that the color laser printer 30 has to execute four times the operations of: charge disposition, emitting laser beams onto the image roller 32 and forming an electrostatic image, attracting toner contained in each of the toner cartridges 38Y, 38C, 38M and 38K with the electrostatic image, transferring the image, and discharging charges and feeding the printing media 31 through the fuser 44 to melt and adhere the toner. Such quantity of operations executed by the color laser printer 30 is time-consuming.
Please refer to FIG. 3, which is a schematic diagram of a Tandem color laser printer 50 according to the prior art. The color laser printer 50 comprises a fuser 64, four toner cartridges 58Y, 58C, 58M and 58K for containing yellow, cyan, magenta and black toner respectively, and four corresponding developer rollers 60Y, 60C, 60M and 60K. In contrast to the Carousel color laser printer 30, the Tandem color laser printer 50 comprises four image rollers 52Y, 52C, 52M and 52K, four charged rollers 54Y, 54C, 54M and 54K, four laser beam units 56Y, 56C, 56M and 56K, and four transfer rollers 62Y, 62C, 62M and 62K. Four printing medias are disposed between the transfer rollers 62Y, 62C, 62M and 62K and corresponding image rollers 52Y, 52C, 52M and 52K respectively.
The color laser printer 50 also has principles and operations similar to those of the laser printer 10. The only difference is that the color laser printer 50 executes four times the operations of charge disposition, emitting laser beams onto the corresponding image rollers to form electrostatic images, attracting toner contained in corresponding toner cartridges with the electrostatic image, transferring images and discharging charges simultaneously to attract toner contained in the toner cartridges onto the printing media 51Y, 51C, 51M and 51K respectively. Since the Tandem color laser printer 50 is capable of printing the four printing media 51Y, 51C, 51M and 51K simultaneously, printing four colors of toner onto a printing media equivalently, the Tandem color laser printer 50 runs four times as fast as the Carousel color laser printer 30. However, the color laser printer 50 comprises four toner cartridges, four developer rollers, four image rollers, four charged rollers, four laser beam units, four transfer rollers, and four discharging units to perform with such a high efficiency, and thus, has disadvantages of high-cost and bulk. In addition, the color laser printer 50 cannot dispose toner onto the printing media 51Y, 51C, 51M and 51K precisely unless the laser beam units 56Y, 56C, 56M and 56K all have high quality and function in perfect coordination with the transfer rollers 62Y, 62C, 62M and 62K.